Unsaturated bond recognition leads to biased signal in a fatty acid receptor.

Individual free fatty acids (FAs) play important roles in metabolic homeostasis, many through engagement with more than 40G protein-coupled receptors. Searching for receptors to sense beneficial omega-3 FAs of fish oil enabled the identification of GPR120, which is involved in a spectrum of metabolic diseases. Here, we report six cryo-electron microscopy structures of GPR120 in complex with FA hormones or TUG891 and Gi or Giq trimers. Aromatic residues inside the GPR120 ligand pocket were responsible for recognizing different double-bond positions of these FAs and connect ligand recognition to distinct effector coupling. We also investigated synthetic ligand selectivity and the structural basis of missense single-nucleotide polymorphisms. We reveal how GPR120 differentiates rigid double bonds and flexible single bonds. The knowledge gleaned here may facilitate rational drug design targeting to GPR120.

Tethered peptide activation mechanism of the adhesion GPCRs ADGRG2 and ADGRG4.

Adhesion G protein-coupled receptors (aGPCRs) constitute an evolutionarily ancient family of receptors that often undergo autoproteolysis to produce α and ß subunits1-3. A tethered agonism mediated by the 'Stachel sequence' of the ß subunit has been proposed to have central roles in aGPCR activation4-6. Here we present three cryo-electron microscopy structures of aGPCRs coupled to the Gs heterotrimer. Two of these aGPCRs are activated by tethered Stachel sequences-the ADGRG2-ß-Gs complex and the ADGRG4-ß-Gs complex (in which ß indicates the ß subunit of the aGPCR)-and the other is the full-length ADGRG2 in complex with the exogenous ADGRG2 Stachel-sequence-derived peptide agonist IP15 (ADGRG2(FL)-IP15-Gs). The Stachel sequences of both ADGRG2-ß and ADGRG4-ß assume a U shape and insert deeply into the seven-transmembrane bundles. Constituting the FXφφφXφ motif (in which φ represents a hydrophobic residue), five residues of ADGRG2-ß or ADGRG4-ß extend like fingers to mediate binding to the seven-transmembrane domain and activation of the receptor. The structure of the ADGRG2(FL)-IP15-Gs complex reveals the structural basis for the improved binding affinity of IP15 compared with VPM-p15 and indicates that rational design of peptidic agonists could be achieved by exploiting aGPCR-ß structures. By converting the 'finger residues' to acidic residues, we develop a method to generate peptidic antagonists towards several aGPCRs. Collectively, our study provides structural and biochemical insights into the tethered activation mechanism of aGPCRs.

Ligand recognition, unconventional activation, and G protein coupling of the prostaglandin E2 receptor EP2 subtype.

Selective modulation of the heterotrimeric G protein α S subunit-coupled prostaglandin E2 (PGE2) receptor EP2 subtype is a promising therapeutic strategy for osteoporosis, ocular hypertension, neurodegenerative diseases, and cardiovascular disorders. Here, we report the cryo-electron microscopy structure of the EP2-Gs complex with its endogenous agonist PGE2 and two synthesized agonists, taprenepag and evatanepag (CP-533536). These structures revealed distinct features of EP2 within the EP receptor family in terms of its unconventional receptor activation and G protein coupling mechanisms, including activation in the absence of a typical W6.48 "toggle switch" and coupling to Gs via helix 8. Moreover, inspection of the agonist-bound EP2 structures uncovered key motifs governing ligand selectivity. Our study provides important knowledge for agonist recognition and activation mechanisms of EP2 and will facilitate the rational design of drugs targeting the PGE2 signaling system.

Ligand recognition and allosteric regulation of DRD1-Gs signaling complexes.

Dopamine receptors, including D1- and D2-like receptors, are important therapeutic targets in a variety of neurological syndromes, as well as cardiovascular and kidney diseases. Here, we present five cryoelectron microscopy (cryo-EM) structures of the dopamine D1 receptor (DRD1) coupled to Gs heterotrimer in complex with three catechol-based agonists, a non-catechol agonist, and a positive allosteric modulator for endogenous dopamine. These structures revealed that a polar interaction network is essential for catecholamine-like agonist recognition, whereas specific motifs in the extended binding pocket were responsible for discriminating D1- from D2-like receptors. Moreover, allosteric binding at a distinct inner surface pocket improved the activity of DRD1 by stabilizing endogenous dopamine interaction at the orthosteric site. DRD1-Gs interface revealed key features that serve as determinants for G protein coupling. Together, our study provides a structural understanding of the ligand recognition, allosteric regulation, and G protein coupling mechanisms of DRD1.

Structures of the glucocorticoid-bound adhesion receptor GPR97-Go complex.

Adhesion G-protein-coupled receptors (GPCRs) are a major family of GPCRs, but limited knowledge of their ligand regulation or structure is available1-3. Here we report that glucocorticoid stress hormones activate adhesion G-protein-coupled receptor G3 (ADGRG3; also known as GPR97)4-6, a prototypical adhesion GPCR. The cryo-electron microscopy structures of GPR97-Go complexes bound to the anti-inflammatory drug beclomethasone or the steroid hormone cortisol revealed that glucocorticoids bind to a pocket within the transmembrane domain. The steroidal core of glucocorticoids is packed against the 'toggle switch' residue W6.53, which senses the binding of a ligand and induces activation of the receptor. Active GPR97 uses a quaternary core and HLY motif to fasten the seven-transmembrane bundle and to mediate G protein coupling. The cytoplasmic side of GPR97 has an open cavity, where all three intracellular loops interact with the Go protein, contributing to the high basal activity of GRP97. Palmitoylation at the cytosolic tail of the Go protein was found to be essential for efficient engagement with GPR97 but is not observed in other solved GPCR complex structures. Our work provides a structural basis for ligand binding to the seven-transmembrane domain of an adhesion GPCR and subsequent G protein coupling.

[Design and application of the expanded transposition flaps in the treatment of cheek skin defects].

OBJECTIVE: To introduce the design and application of the expanded transposition skin flap in the treatment of cheek skin defects. METHODS: The expanded transposition flaps were divided into three types: the regular expanded transposition flap (ERT flap), the expanded transposition-advancement-transposition flap (TAT flap) and the expanded rotation-advancement-transposition flap (RAT flap). 135 cases of cheek skin defects resulted from hemangioma, scar and naevi were treated with these three types of flaps. Delay surgery was needed when the ratio of length to width was bigger than 2 : 1. RESULTS: There were 139 expanded transposition flaps, including 17 ERT flaps, 69 TAT flaps, 53 RAT flaps. Blood supply disturbance was happened at the end of the flaps in 6 cases, including 2 ERT flaps and 4 other flaps. Other flaps had no complication. The results were satisfactory. CONCLUSIONS: The expanded transposition skin flap is a reliable method to repair the cheek skin defect. The preoperative flap design is very important for successful reconstruction.